thevirginian

A buddy of mine fried his Evolution 116 GX2 for the third time in his H9 260 Extra. He has no baffle, simply because he doesn't believe in baffling the cowl. After tthe first engine seisure I told him to install a baffle. He gaffed it off. Then he cooked the motor again and still wouldn't heed my advise. After the second time he even machined a relief on top of both pistons. I told him that this would not help against overheating and sure enough, yesterday, he fried the engine again. Now he is talking about a DA100. I told him that he will run into the same problems again. I still believe he must baffle the cowl. What is you guys opinion? Am I right or could it be something else?

fancman

My Feedback: (16)

Adding a baffle is certainly a good thing to do but it shouldn't be necessary if the air intake and exit areas of the cowl are large enough to provide sufficient air flow. The air exit point of the cowl should be roughly four times the size of the intake. I believe that the generaly accepted figure.

I don't know how much experience your friend has with gas engines but he could also be running the engines lean. That would sieze them as well as insufficient cooling. Sounds like a case of more money than ($&%(s.

mrbigg

My Feedback: (21)

Foolish on his part. His tuning skills seem to be off also. Have him rebuild it and fly it without the cowl. Then he can put the cowl back on, lock it up, and prove you right.

Jake Ruddy

My Feedback: (40)

Since it is a twin the rule of twice the exit of air doesn't properly cool the engine. On a single the head is usually at the bottom of the cowl so more air is forced through the fins.

On a twin depending what the distance from the cowl to the fins are, the air my very well only cool the front of the fin and most definately not the top or back of the fins. Air is going to take the path of least resistance and in this case that means around the fins and not through them. A baffle will force the air through the fins and cool it properly.

Everyone else is correct though, lean running will speed up this process.

Tired Old Man

My Feedback: (1)

You would think after cooking off three engines the guy would have learned something by now. Going with a DA or any other engine type will not change his luck unless he changes his ways.

altavillan

My Feedback: (1)

The guy is obviously baffled by brilliance (his own). Determined to prove he will succede where everyone else has failed, and will no doubt be the next "xspurt" here as soon as he can succesfully complete one Sunday of flying.

qldviking

Definately more money than sense, he either doesnt have enough venting, the venting needs baffles or running lean, most likely all 3. seems he needs some attitude adjustment as well

thevirginian

No, he ran the motor rather rich. But he doesn't believe in proper break-in procedures for gas engines either. He likes to fly WOT.

Bad Tooth

My Feedback: (10)

Hey guys, I don't fly any gas, just nitro........and the only "baffle" I know of is in my glow muffler. Would someone explain what the baffle is in a cowl on a gas engine?

Thanks.

Jake Ruddy

My Feedback: (40)

Well sounds like the old, you can lead a horse to water but you can't make them drink...

Maybe after he wastes enough money he will listen... however if you are still flying WOT all the time by the time you move to GS planes chances are you don't listen anyhow because someone has surely told you 20 times by now that there is a left stick that controls speed and this cool thing called the rudder.

qldviking

A baffle is just ducting to force air through the cooling fins of the motor, so the air doesnt run around the outside with no cooling effect. I usually use very light guage alloy sheet, some use stainless, even 1/16" ply, doesnt really matter as long as the air is going through the fins, not past them

Jake Ruddy

My Feedback: (40)

Sorry I dont have a pic handy.

However a baffle is used to direct airflow.

For example if you had a twin motor with 2 cylinder heads you can see through the air intakes (around the spinner) you would make a plate that extends the inside of the cowl towards to the cylinders. This would make it so the air couldn't just down down the front inside of the cowl, it would have to go through the cooling fins on the motor and then out the bottom of the cowl.

qldviking

Sounds like a real turkey, and I bet when he fries the DA he'll then blame the airframe. He should go back to flying paperplanes, at least then he wont be destroying good equipment through stupidity

fancman

My Feedback: (16)

Here is a link to an article about baffles. I've owned three 100CC engines and never had an overheating problem with any of them without using baffles. I did however make sure I had sufficient cooling air inlet and outlet size. Baffles are better but any gas engine can be flow and cooled effectively without them as long as your basic setup is correct.

http://cactusaviation.com/Tech/baffling.html

qldviking

He sounds like someone I DONT want to share an airfield with

pe reivers

to baffle or not to baffle is a no brainer.
Glow engines get away without baffles, gas engines will not. They need baffles. Even the engines flown without cowl will get too hot, unless flown without long uplines.
Our engines just have the fins too small to get rid of the heat that all the power generates.

So bafle your engine, or be sorry.

thevirginian

If he doesn't listen to me I hope at least he would read this thread.

qldviking

if your buddy is that much of a turkey that he wont listen and do a simple job of putting in a baffle he sure as h**l aint gonna sit down and read this

pe reivers

Yep think outside the circle as well, or any fenced mind corral, as long as thinking is done.
Plain braindead noncense won't cut the cake with gas engines. They are a man's plane engine, and no toys by a long shot.

thevirginian

O.K. here are the latest results after investigating this malfunction. Actually the piston hasn't seized. It has a hole burned thru the top. The cylinder wall doesn't show any scuff marks, which would have indicated seizure from heat. The cylinders are O.K., only a hole in the center of the piston top. Pretty weird. So, he ordered already a set of new pistons with rings and is going to replace them. Baffling? No, he still believes it's not necessary.

qldviking

burnt out pistons are usually a combination of running lean and hot, are the cylinders discoloured on the outside? what colour where the plugs? are the plugs the right heat range? all these are capable of burning holes in pistoms quite quickly

DadsToysBG

My Feedback: (35)

Had some issues with heat on my plane. Temps in the high 190's. Now after putting in the baffles temps are down in the 150's. Bobby at Cactus made a believer out of me. Dennis

altavillan

My Feedback: (1)

Low octane will lead to burn holes in pistons as quick as over heating from running lean. Though in this case I suspect low octane gas is the culprit. Pre-ignition will concentrate the heat in one spot. Fresh gas is a must. The more octane the better.

Tired Old Man

My Feedback: (1)

I think the guy needs to go back to .40 glow engines. Anyone burning holes in a piston is doing EVERYTHING wrong. The manufacturers love this type of person because they buy lots of parts, all the time.

pe reivers

Altavillan, I fully agree with you, but suspect that running too lean also helped, along with too little cooling.
In general:
Pistons don't necessarily seize or scuff when an engine gets too hot. Our modern oils are good at preventing that. The cylinder expands along with the piston, until temperatures rise such, that the metal cannot support the combustion pressure any more. (talking about aluminum cylinders here).
Pistons that seize, probably have too much play to begin with so they cannot transfer their heat to the cylinder on the complete circumference. When stuff gets nasty, everything goes out of round, and local high spots will scuff and finally seize.